The field of the invention generally relates to automatic washing machines, and more particularly relates to a brake and release mechanism for a washing machine having an alternately reversing drive motor.
In the most common arrangement of prior art automatic washing machines, a reversible drive motor is connected to a reciprocating transmission with a drive belt. When the motor drives the input shaft of the transmission in one direction, here designated clockwise for convenience of discussion, the transmission provides reciprocating motion to its output shaft which is connected to the washer agitator located within the spin tub or clothes basket. That is, in response to a uni-directional clockwise drive, the output shaft of the transmission oscillates back and forth through a predetermined arc thus providing an agitator stroke. When the drive motor is driven in the opposite or counterclockwise direction, the spin tub is rapidly rotated to centrifugally extract washing fluid from the clothes during a spin cycle. Typically, a brake is engaged so that the spin tub will not rotate during an agitate cycle, and the brake is released when the motor is reversed (i.e. driven in the counterclockwise direction) to provide the rapid spinning of the spin tub. The brake is also used at the end of the spin cycle to stop the spin tub from spinning.
One prior art brake mechanism is described in U.S. Pat. No. 3,838,755. The brake mechanism includes a pair of generally flat circular plates adapted to be moved axially relative to one another to frictionally compress one or more stationary brake pads wherein one of the plates is fixed to a shaft connected to the spin tub. A conical spring is positioned adjacent the moveable plate and urges that plate towards the other plate so as to clamp the brake pads. Deflection of the inner periphery of the conical spring causes its outer periphery to move away from the axial moveable plate, thereby releasing the braking force applied to the brake pads positioned between the two plates. The brake mechanism is then free to rotate with the spin tub shaft. By permitting the inner periphery of the conical spring to return to its undeflected positioned, the braking force is reapplied to prevent rotation of the spin tub shaft.
In order to release the brake of the above described mechanism, the driven pulley has an underside hub that has helical surfaces that are supported on a conforming helical washer. When the driven pulley rotates in the clockwise direction, the pulley remains in a down position and drives the helical washer which has an internal surface coupled to the input shaft to the transmission. However, when the driven pulley rotates in the counterclockwise direction, it rides up on the inclined surfaces of the helical washer and pushes up against the conical spring thereby deflecting it and releasing the brake. In other words, when the motor drives in one direction, the brake is engaged; and when the motor drives in the opposite direction, the brake is mechanically released.
The above described brake release mechanism has a drawback, however, in that it is not applicable to a relatively new washer design that uses a permanent split capacitor motor. More specifically, permanent split capacitor motors have recently been used to drive commercially available washers. Such motors have a significant advantage in that their rotational direction can be reversed quickly enough so that expensive reciprocating transmissions are no longer required. In other words, the direction reversal for the agitate mode comes directly from the motor rather than driving a reciprocating transmission unidirectionally. The above described brake release mechanism is not applicable to such permanent split capacitor motor arrangements because such release mechanism depends on a shaft being driven in one direction for agitate and in the opposite for spin. As a result, prior art washers with permanent split capacitor motors have used expensive solenoids to release the brake so as to initiate a spin cycle.